The present disclosure relates to devices which electrically generate, display, or record still images and moving images, such as imaging elements used in digital still cameras, digital camcorders, or mobile camera telephones.
For recent digital still cameras, there has been a trend toward enhancing the function of capturing high-definition still images using a single-color-solid-state-sensor imaging element having a larger number of pixels, and significant advances have been made in that function. Meanwhile, for digital still cameras whose main function is to capture still images, higher image quality and higher performance have also been required for the function of capturing and recording moving images, which is conventionally a secondary function, particularly as HDTV players and televisions have become widespread. Under these circumstances, a pixel binning technique capable of simultaneously achieving high-definition still images and high-quality moving images has been proposed which is implemented by a method of driving an imaging element or an internal structure of an imaging element (see Japanese Patent Publication No. 2004-312140).
However, in cameras which have a high-definition solid-state imaging element which requires high focusing accuracy and therefore require lens focus adjustment, if the pixel binning technique is employed in the solid-state imaging element in order to generate high-quality moving images during recording of moving images, a spatial low-pass filter (LPF) inevitably emerges, leading to attenuation of high spatial frequency components which can be recorded in the case of still images. Therefore, when the pixel binning operation is performed in the imaging element, it is difficult to perform lens focus adjustment which ensures focusing accuracy for capturing still images.
To solve this problem, a technique of performing so-called contrast AF has been proposed as follows. When a moving image generation mode is transitioned to a still image generation mode, control is temporarily transitioned to a mode (skip/read mode) in which information is read from all pixels in one of the horizontal and vertical directions without performing pixel binning in the solid-state imaging element, and reading is skipped for some pixels in the other direction. In this mode, the lens focus is adjusted by extracting spatial frequency components in a band required for ensuring the focusing accuracy of still images using pixel signals in the direction in which information is read from all pixels while shifting the focus position of the lens by a predetermined amount (see Japanese Patent Publication No. 2005-92081).